2,379 research outputs found
Frequency Dependence of Aging, Rejuvenation and Memory in a disordered ferroelectric
We characterize in details the aging properties of the ferroelectric phase of
K Ta_{1-x} Nb_x O_3 (KTN), where both rejuvenation and (partial) memory are
observed. In particular, we carefully examine the frequency dependence of
several quantities that characterize aging, rejuvenation and memory. We find a
marked subaging behaviour, with an a.c. dielectric susceptiblity scaling as
, where is the waiting time. We suggest an
interpretation in terms of pinned domain walls, much along the lines proposed
for aging in a disordered ferromagnet, where both domain wall reconformations
and overall (cumulative) domain growth are needed to rationalize the
experimental findings.Comment: submitted to EPJ
Sputtering of Oxygen Ice by Low Energy Ions
Naturally occurring ices lie on both interstellar dust grains and on
celestial objects, such as those in the outer solar system. These ices are
continu- ously subjected to irradiation by ions from the solar wind and/or
cosmic rays, which modify their surfaces. As a result, new molecular species
may form which can be sputtered off into space or planetary atmospheres. We
determined the experimental values of sputtering yields for irradiation of
oxygen ice at 10 K by singly (He+, C+, N+, O+ and Ar+) and doubly (C2+, N2+ and
O2+) charged ions with 4 keV kinetic energy. In these laboratory experiments,
oxygen ice was deposited and irradiated by ions in an ultra high vacuum chamber
at low temperature to simulate the environment of space. The number of
molecules removed by sputtering was observed by measurement of the ice
thickness using laser interferometry. Preliminary mass spectra were taken of
sputtered species and of molecules formed in the ice by temperature programmed
desorption (TPD). We find that the experimental sputtering yields increase
approximately linearly with the projectile ion mass (or momentum squared) for
all ions studied. No difference was found between the sputtering yield for
singly and doubly charged ions of the same atom within the experimental
uncertainty, as expected for a process dominated by momentum transfer. The
experimental sputter yields are in good agreement with values calculated using
a theoretical model except in the case of oxygen ions. Preliminary studies have
shown molecular oxygen as the dominant species sputtered and TPD measurements
indicate ozone formation.Comment: to be published in Surface Science (2015
The Formation of the Collisional Family around the Dwarf Planet Haumea
Haumea, a rapidly rotating elongated dwarf planet (~ 1500 km in diameter),
has two satellites and is associated with a "family" of several smaller Kuiper
Belt objects (KBOs) in similar orbits. All members of the Haumea system share a
water ice spectral feature that is distinct from all other KBOs. The relative
velocities between the Haumea family members are too small to have formed by
catastrophic disruption of a large precursor body, which is the process that
formed families around much smaller asteroids in the Main Belt. Here we show
that all of the unusual characteristics of the Haumea system are explained by a
novel type of giant collision: a graze-and-merge impact between two comparably
sized bodies. The grazing encounter imparted the high angular momentum that
spun off fragments from the icy crust of the elongated merged body. The
fragments became satellites and family members. Giant collision outcomes are
extremely sensitive to the impact parameters. Compared to the Main Belt, the
largest bodies in the Kuiper Belt are more massive and experience slower
velocity collisions; hence, outcomes of giant collisions are dramatically
different between the inner and outer solar system. The dwarf planets in the
Kuiper Belt record an unexpectedly large number of giant collisions, requiring
a special dynamical event at the end of solar system formation.Comment: Accepted for publication in ApJ, 12 pages, 4 figures, 2 tables
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua
During the formation and evolution of the Solar System, significant numbers of cometary and asteroidal bodies were ejected into interstellar space. It is reasonable to expect that the same happened for planetary systems other than our own. Detection of such interstellar objects would allow us to probe the planetesimal formation processes around other stars, possibly together with the effects of long-term exposure to the interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known interstellar object, discovered by the Pan-STARRS1 telescope in October 2017. The discovery epoch photometry implies a highly elongated body with radii of ~ 200 × 20 m when a comet-like geometric albedo of 0.04 is assumed. The observable interstellar object population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity of 'Oumuamua implies a lack of surface ice. Here, we report spectroscopic characterization of ‘Oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer Solar System. We show that this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure. An internal icy composition cannot therefore be ruled out by the lack of activity, even though ‘Oumuamua passed within 0.25 au of the Sun
Electrical and raman scattering studies of ZnO:P and ZnO:Sb thin films
A study on the structure, electrical and optical properties of ZnO thin films produced by r.f. magnetron sputtering and implanted either with phosphorous (P) or antimony (Sb) is reported in this work. Raman spectroscopy, X-ray diffraction, optical transmittance and Hall effect measurements have been employed to characterize the samples. X-ray diffraction and Raman scattering patterns confirm that, after a 500ºC annealing, the doped films keep a polycrystalline nature with (002) preferred orientation. These films are very transparent and Hall effect results show that all have p-type conduction, despite doping ion and dose. The electric resistivity reaches values of 0.012 (cm) and 0.042 (cm) for the P and Sb-doped samples, respectivel
Prevalência de infecção latente pelo Mycobacterium Tuberculosis entre profissionais de saúde da Atenção Básica no MunicÃpio de Vitória, ES
Apesar de ser uma das mais importantes causas de morbimortalidade no mundo, a
Tuberculose (TB) continua sendo um problema negligenciado nos paÃses em
desenvolvimento e um importante agravo na Saúde Pública, evidenciado pela sua
transcendência, magnitude e vulnerabilidade. Além disso, a coinfecção pelo VÃrus da
Imunodeficiência Humana (HIV) e o aparecimento de cepas resistentes configuramse
em novas barreiras e importantes desafios a serem enfrentados mundialmente.
Entre os grupos de risco de infecção, os profissionais da área da saúde são dos
mais vulneráveis, como já demonstrado em algumas publicações. Em 2004, o
Ministério da Saúde enfatizou a integração das atividades do Programa Nacional de
Controle da TB (PNCT) para todos os serviços do Sistema Único de Saúde (SUS)
seguindo suas diretrizes de horizontalização e descentralização no combate à TB.
Trata-se de um estudo de corte transversal, no qual as informações foram obtidas
por meio de um questionário, com questões abertas e fechadas, sobre dados
sociodemográficos, ocupacionais, clÃnicos, de exposição e conhecimento sobre
tuberculose. Foi aplicado o teste tuberculÃnico avaliado após 72 horas, por
profissional capacitado, e seu resultado baseou-se em pontos de corte positivos de
10mm e de 5mm de enduração. Participaram 226 voluntários e resultou em uma
perda de 2,1%. Foi obtida uma prevalência de positividade ao teste de 40,7% e de
54,9% para ambos os pontos de corte. A associação entre o intervalo de tempo de
exercÃcio ≥ 5 anos e o TST para o ponto de corte de 5mm mostrou-se
estatisticamente significante (p = 0). Apesar da tendência de declÃnio na incidência
da TB, conclui-se que os profissionais de saúde estão expostos a essa doença.
Diante do desinteresse do Ente Público e, consequentemente, no impacto da
biossegurança, há necessidade de que sejam reforçadas politicamente ações
efetivas de impactos na Saúde do Trabalhador da Atenção Primária voltadas para
esses profissionais
New core and spectrum balancing algorithms for space division multiplexed elastic optical networks
This paper proposes two new algorithms for core and spectrum allocation in Elastic Optical Networks with Space Division Multiplexing. In order to avoid the effect of inter-core crosstalk, a Core Balancing Algorithm (CBA) is proposed for core allocation, and a Spectrum Balancing Algorithm (SBA) for spectral allocation. Such algorithms prove to be efficient in terms of circuit blocking probability and blocked data ratio. They achieve at least 55.7% gain in terms of circuit blocking probability and 41.1% gain in terms of blocked data ratio when compared to other evaluated algorithms. It is shown that the proposed algorithms achieve low computational cost and higher energy efficiency than other similar algorithms.info:eu-repo/semantics/acceptedVersio
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